The present invention relates to a conveyor for effecting a conveyance of a workpiece between a plurality of vacuum containers such as a CVD apparatus, an etching apparatus, a sputtering apparatus, a testing apparatus and the like for manufacturing electronic devices such as semiconductor integrated circuits or the like.
A high level vacuum atmosphere has been widely used in a manufacturing apparatus or a testing apparatus for electronic devices such as semiconductor circuits. A structure of a mechanism for effecting a predetermined operation or work under such circumstances should not have any contact portion such as a sliding contact portion or a rolling contact portion. This is because fine particles, discharged gas or the like generated by the friction at the contact portion would cause degradation of the vacuum level or contamination of the vacuum atmosphere. For this reason, the conventional conveyor to be disposed in the vacuum chamber is so constructed not to have any contact portion.
The conventional conveyor will now be described with reference to FIGS. 10 through 13.
A sleeve-like partition wall 1 having a circular shape in cross section is provided within a vacuum chamber. A space on an inner circumferential surface 1a side of the partition wall 1 is kept at an atmospheric level. A floating member 3 having a conveying rod 2 is provided on an outer circumferential surface 1b side of the partition wall 1. The floating member 3 has a diameter somewhat larger than an outer diameter of the partition wall 1 with its inner circumferential surface 3a facing the outer circumferential surface 1b of the partition wall 1. On the other hand, a conveying body 4 magnetically coupled with the floating member 3 is disposed on the inner circumferential surface 1a side of the partition wall 1. The conveying body 4 has a diameter somewhat smaller than an inner diameter of the sleeve-like partition wall 1 with its outer circumferential surface 4a facing the inner circumferential surface 1a of the partition wall 1. The conveying body 4 is mounted reciprocatingly movable along a guide rail 9 which in turn is laterally provided between both ends of the partition wall 1 through an opening portion 10 of the conveying body 4. Furthermore, a linear motor coil 11 is disposed within the opening portion 10 of the conveying body 4. A motor secondary conductor 12 is provided so as to face a linear motor coil 11 on the guide rail 9. Also, the partition wall 1 is coupled with a rotary shaft 14 through a support member 13.
In the conveyor thus constructed, the conveying body 4 is moved between both the ends of the partition wall 1 along the guide rail 9 by the linear motor coil 11 and the motor secondary conductor 12 that constitute a drive source and is further rotated in cooperation with the rotation of the rotary shaft 14. The conveying rod 2 is mounted on the floating member 3 that is magnetically coupled with the conveying body 4, and hence the conveying rod 2 will follow the movement of the conveying body 4. Namely, the linear movement and the rotary motion which are needed for conveyance of the workpiece 19 are carried out without any contact portion.
The magnetic support portion which magnetically couples the conveying body and the floating member through the partition wall will now be described in more detail.
As shown in FIGS. 10 and 11, two electromagnets 6 and 16 are disposed on the outer circumferential surface 4a of the conveying body 4 so as to face the inner circumferential surface 1a of the partitioning surface on each of a V-axis or a W-axis, respectively, at a rear end portion of the conveying body 4. Also, two sensor portions 8 and 18 are disposed in the vicinity of the positions on the V-axis and W-axis on the outer circumferential surface 4a of the conveying body 4 for detecting the floating position of the floating member 3 on each axis. Targets 7 and 17 made of magnetic material are provided on the inner circumferential surface of the floating member where the targets face the associated electromagnets 6 and 16. The magnetic support portions 5 and 15 are constituted by the electromagnets 6 and 16, the targets 7 and 17 and the sensor portions 8 and 18, respectively.
It should be noted that the V-axis and W-axis are slanted at about 45.degree. with respect to the horizontal axis. In this case, the horizontal and vertical components are balanced at 1:1, so that its control may be easy but it is possible to control the conveying mechanism even at any other slant angle.
The front end portion of the conveying body 4 is constituted in the same way as in the rear end portion described above. Accordingly, four electromagnets and sensor portions are provided on each end portion of the conveying body 4, and in total eight electromagnets and sensor portions are provided in the conveying body 4.
FIGS. 12 and 13 show a conveyor where magnetic support portions are provided only on the lower side of both end portions of the conveying body. In this case, the electromagnets 26 are provided on the outer circumferential surface 4a of the conveying body 4 so as to face the inner circumferential surface 1a of the partition wall on the lower side on the V-axis and W-axis at the front end portion of the conveying body 4, respectively. Two sensor portions 28 and 38 are provided in the vicinity of each axis on the outer circumferential surface side of the conveying body 4 for detecting the floating position of the floating member 3 on each axis. Also, targets 27 made of magnetic material are provided on the inner circumferential surface 3a of the floating member 3 so as to face the associated electromagnets 26. The magnetic support portions 25 are constituted by the electromagnets 26, the targets 27 and the sensor portions 28 and 38. The rear end portion of the conveying body 4 is constructed in the same way as in the front end portion.
However, in the conventional apparatus shown in FIGS. 10 and 11, in order to hold the floating member, the sum of the control current for the electromagnets for each axis is controlled to be constant. For this reason, even if the conveying article load (i.e., the workpiece weight) would be small, the consumption current would not be changed. As a result, the heat generation amount would be increased exceeding the necessary level. Thus, it is disadvantageous that a temperature of the partition wall would be elevated, as a result of which the gas generation amount would be increased.
On the other hand, in the conventional apparatus shown in FIGS. 12 and 13, since the above-described disadvantages might be solved since the current will flow in accordance with the load of the conveying article. Nevertheless, the system suffers from another disadvantage that a possible conveying weight would be decreased. Namely, when the article is laid, a moment would be effected in the magnetic support portion on the rear end lower portion in a direction where a space between the target and the electromagnet is decreased. On the other hand, in the magnetic support portions, the magnetic force which is effected between the targets and the electromagnets is an attractive force generated by the control current. This attractive force is exerted in the same direction as that of the above-described moment. Accordingly, with such conveyor, it is impossible to effect the force in the direction opposite the moment force. For this reason, it is impossible to control the apparatus so as to float in parallel even if the attractive force is interrupted by stopping the electromagnet control current, if the conveying article load becomes large to bring the targets and the electromagnets into contact with each other. As described above, since it would be impossible to control the rear end portion in the case where the weight of the article is increased in the conveyor which has the magnetic support portions only on the lower side of the front and rear portions, the possible conveying weight is decreased in comparison with the apparatus having the magnetic support portions on the upper side as shown in FIGS. 10 and 11.